The present invention relates to the art of fabrication of board, and more particularly to fabrication of board from fibrous material of vegetable origin. The invention can be used most advantageously in fabrication of multilayer boards, such as container board used to form smooth layers of corrugated board, box board used to make boxes for packing consumer goods and food products, ticket and innersole boards used, respectively, to make tickets and as an alternative to leather innersoles of shoes.
As is known, according to processing technique boards are classified into single-layer and multilayer ones.
Materials usable as a fibrous material for board manufacturing are cellulose, hemicellulose, wood pulp, and scrap materials. Single-layer boards are manufactured by applying a layer of pulp onto a endless wire screen of a board making machine.
Boards consisting of two and more layers are fabricated by successively applying the first and subsequent layers onto the wire screen, or by combining separate board layers made on a cylinder machine and by pressing them together, the outside layers being termed surface layers and the inside layers being termed base layers. If a board is a two-layer one, the upper layer is termed a surface layer and the bottom one is termed a base layer.
According to its composition, a single-layer board is made from a single material of vegetable origin or from a mixture of a few kinds of materials. Two-layer and multilayer boards may be made of material of the same kind or have a multicomponent composition with various relations between the components in different layers. For outside surface layers are used fine traditional materials of high quality. Materials used for base layers are materials of lower grade. The use of low-grade materials for inside layers makes it possible to decrease the consumption of high-quality fibrous materials and to cut down the cost of the board, its main properties being retained. However, fabrication of a board requires in general a substantial amount of materials of vegetable origin.
Known in the art is a multilayer board (cf. Author's Certificate of the U.S.S.R. No. 566,897, Int. Cl. D21H 1/100, 5/100, issued July 30, 1977) which contains in its surface and base layers fibrous material of vegetable origin in the amount of 98.69% by mass.
To improve physicomechanical properties of the board, into the base layers are introduced sodium aluminate and talc. However, fabrication of such a board requires only the material of vegetable origin.
Widely known are kinds of board wherein, to save costly cellulose fiber, a substantial amount thereof is substituted by scrap material.
However, scrap material represents used-up fibrous material which is also a material of vegetable origin and hence it does not solve the problem of saving this material. To this end, investigations were made to reduce the consumption of vegetable materials by substitution thereof by less costly components.
According to Author's Certificate of the U.S.S.R. No. 440,468, Int. Cl. D21H 3/100, issued Aug. 25, 1974, introduced into a pulp prior to layer forming is some amount of activated sludge which is obtained as a waste product of biological sewage treatment. Fabrication of board from the pulp containing fibrous material and sludge made it possible to obtain less costly board. However, the process of board fabrication with activated sludge introduced directly into the pulp has a number of serious disadvantages. When such a board is made on a board making machine, a substantial amount of the sludge falls through a wire screen, i.e. fabrication of the board with maximum sludge retention is rather difficult. To reduce the amount of sludge falling through the wire mesh and to intensify water removal the use of chemical agents is required. Without the use of such agents, fine sludge particles fall through the wire screen of a paper making machine. The sludge particles adsorbed on fibers impede water removal. At the same time, tray water is contaminated by suspended particles and the load on local treatment facilities is thus increased whereby the consumption of chemical agents for sewage treatment is also increased.